Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$40.41	3.718%	$41.9124	$41.91	$41.90	$41.90
Purchase #2	$71.45	7.849%	$77.0581	$77.06	$77.05	$77.10
Purchase #3	$32.76	7.501%	$35.2173	$35.22	$35.20	$35.20
Purchase #4	$9.91	5.842%	$10.4889	$10.49	$10.50	$10.50
Purchase #5	$249.41	3.659%	$258.5359	$258.54	$258.55	$258.50
Purchase #6	$210.81	9.229%	$230.2657	$230.27	$230.25	$230.30
Purchase #7	$33.30	7.841%	$35.9111	$35.91	$35.90	$35.90
7 purchase totals =	$648.05		$689.3894	$689.40	$689.35	$689.40